Pumping of caustic or abrasive fluids may be achieved by way of centrifugal pumps in a variety of industries. For example, a centrifugal pump may be employed in oilfield operations to deliver, mix, or otherwise maintain an abrasive fluid such as a cement slurry. This is often the case where the cement slurry is to be circulated and maintained by a centrifugal pump in advance of its delivery to a high pressure pump for a cementing application in the oilfield.
Unfortunately, the abrasive fluid may wear down bearings and other wear-sensitive of the centrifugal pump upon exposure thereto. Generally, however, the slurry is prevented from contacting the wear-sensitive parts, by the presence of one or more seals of a conformable polymer or other material provided at the interface of the shaft and the impeller housing. In this way, the cement slurry may be retained inside the impeller housing, and may be occluded from access to the bearings and other components. Unfortunately, however, configurations for centrifugal pumps employed in the oilfield industry leave the seals susceptible to degradation by the abrasive cement slurry.
In spite of the susceptibility of the seals to abrasive wear as noted above, pumping of cement slurry in the oilfield industry is generally achieved by placement of the centrifugal pump, or a substantial portion thereof in direct contact with the cement slurry to be pumped. As a result, a substantial portion of the centrifugal pump, including the above described seals, remains in contact with the slurry during an oilfield cementing application in which a centrifugal pump is employed.
Regular delivery of lubricant to the seals may be provided in order to enhance their functionality. This may also help to preserve integrity of the seals in light of the contact by the cement slurry. Regardless of the seal implementation, however, seals typically wear much more quickly than other parts of the pump. By way of comparison, seals for a centrifugal pump use are likely to become ineffective at up to about ten times the rate or more of other pump parts. Therefore, the pump remains susceptible to catastrophic failure due to seal failure and subsequent bearing failure. Such failures may lead to downtime at the oilfield, at considerable cost to the operator.
Efforts may be undertaken to avoid seal degradation. For example, in other industrial settings outside of the oilfield industry, a centrifugal pump may be configured with a housing for the bearings distanced far from the impeller housing by employing an extended shaft therebetween. In such a configuration, any seals at the interface of the impeller housing and the shaft may be eliminated. Rather, seals may be positioned at the interface of the bearing housing and the shaft in order to provide protection to the bearings therein.
Unfortunately, even for embodiments employed outside of the oilfield industry, moving the seal position up the shaft may not be enough to avoid contact with an abrasive fluid being pumped through the centrifugal pump. For example, depending on the viscosity of the fluid being pumped it is often likely that a fluid such as a cement slurry will climb the shaft at the space between the shaft and its housing. This would be a likely result when pumping an abrasive fluid such as the noted cement slurry. Thus, such embodiments may be undesirable for pumping of cement. Furthermore, the seals remain prone to degradation by such abrasive fluids, thereby leaving the bearings and ultimately the pump itself susceptible to catastrophic failure. Of even greater concern when employing such pumps may be the amount of time and expense devoted to pump maintenance and clean-out following an application, especially where the abrasive is cement.